Image pickup optical system and image pickup apparatus using the same

ABSTRACT

An image pickup optical system made of five lenses, includes in order from an object side, an aperture stop, a first lens L 1  having a positive refracting power, a second lens L 2  having a negative refracting power, a third lens L 3  having a positive refracting power, a fourth lens L 4  having a positive refracting power, and a fifth lens L 5  having a negative refracting power. Moreover, an image pickup apparatus includes this image pickup optical system.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a divisional of U.S. patent application Ser.No. 13/473,045 filed on May 16, 2012, which is a divisional of U.S.patent application Ser. No. 12/660,127 filed on Feb. 18, 2010, now U.S.Pat. No. 8,203,796 which is based upon and claims the benefit ofpriority from the prior Japanese Patent Application No. 2009-042011filed on Feb. 25, 2009; the entire contents of which are incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image pickup optical system and animage pickup apparatus using the same.

2. Description of the Related Art

In recent years, a camera module in which, a thickness in an opticalaxial direction of an optical system is thinned to the maximum withthinning of a cellular telephone has been sought.

Moreover, with an increase in a size and the number of pixels of animage pickup element in recent years, a lens having a high resolutionhas been sought. In order to meet this demand, a single focus opticalsystem which includes about three to five aspheric lenses has beenproposed in Japanese Patent Application Laid-open Publication Nos.2007-264180 and 2007-298572.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, an image pickupoptical system according to the present invention, which is consisted offive lenses, includes in order from an object side

an aperture stop,

a first lens having a positive refracting power,

a second lens having a negative refracting power,

a third lens having a positive refracting power,

a fourth lens having a positive refracting power, and

a fifth lens having a negative refracting power,

in which the image pickup optical system has a fixed focal length, anair space is provided between the second lens and the third lens, and atleast one of surfaces of the fifth lens has an inflection point.

According to a second aspect of the present invention, an image pickupapparatus according to the present invention includes

the abovementioned image pickup optical system, and

an electronic image pickup element having an image pickup surface, and

the image pickup apparatus satisfies the following conditionalexpression15°<αi<30°  (7)

where,

αi denotes an angle of incidence of principal light rays on an imagepickup surface at the maximum image height.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view along an optical axis showing anoptical arrangement at a time of infinite object point focusing of animage pickup optical system according to a first embodiment of thepresent invention;

FIG. 2 is a diagram showing a spherical aberration (SA), an astigmatism(AS), a distortion (DT), and a chromatic aberration of magnification(CC) at the time of infinite object point focusing of the image pickupoptical system according to the first embodiment;

FIG. 3 is a cross-sectional view along an optical axis showing anoptical arrangement at a time of infinite object point focusing of animage pickup optical system according to a second embodiment of thepresent invention;

FIG. 4 is a diagram showing a spherical aberration (SA), an astigmatism(AS), a distortion (DT), and a chromatic aberration of magnification(CC) at the time of infinite object point focusing of the image pickupoptical system according to the second embodiment of the presentinvention;

FIG. 5 is a cross-sectional view along an optical axis showing anoptical arrangement at a time of infinite object point focusing of animage pickup optical system according to a third embodiment of thepresent invention;

FIG. 6 is a diagram showing a spherical aberration (SA), an astigmatism(AS), a distortion (DT), and a chromatic aberration of magnification(CC) at the time of infinite object point focusing of the image pickupoptical system according to the third embodiment of the presentinvention;

FIG. 7 is a cross-sectional view along an optical axis showing anoptical arrangement at a time of infinite object point focusing of animage pickup optical system according to a fourth embodiment of thepresent invention;

FIG. 8 is a diagram showing a spherical aberration (SA), an astigmatism(AS), a distortion (DT), and a chromatic aberration of magnification(CC) at the time of infinite object point focusing of the image pickupoptical system according to the fourth embodiment of the presentinvention;

FIG. 9 is a diagram showing a cross-sectional view along an optical axisshowing an optical arrangement at a time of infinite object pointfocusing of an image pickup optical system according to a fifthembodiment of the present invention;

FIG. 10 is a diagram showing a spherical aberration (SA), an astigmatism(AS), a distortion (DT), and a chromatic aberration of magnification(CC) at the time of infinite object point focusing of the image pickupoptical system according to the fifth embodiment of the presentinvention;

FIG. 11 is a diagram showing a cross-sectional view along an opticalaxis showing an optical arrangement at a time of infinite object pointfocusing of an image pickup optical system according to a sixthembodiment of the present invention;

FIG. 12 is a diagram showing a spherical aberration (SA), an astigmatism(AS), a distortion (DT), and a chromatic aberration of magnification(CC) at the time of infinite object point focusing of the image pickupoptical system according to the sixth embodiment of the presentinvention;

FIG. 13 is a diagram showing a cross-sectional view along an opticalaxis showing an optical arrangement at a time of infinite object pointfocusing of an image pickup optical system according to a seventhembodiment of the present invention;

FIG. 14 is a diagram showing a spherical aberration (SA), an astigmatism(AS), a distortion (DT), and a chromatic aberration of magnification(CC) at the time of infinite object point focusing of the image pickupoptical system according to the seventh embodiment of the presentinvention;

FIG. 15 is a front perspective view showing an appearance of a digitalcamera 40 in which, the image pickup optical system according to thepresent invention is incorporated;

FIG. 16 is a rear perspective view of the digital camera 40;

FIG. 17 is a cross-sectional view showing an optical structure of thedigital camera 40;

FIG. 18 is a front perspective view of a state in which, a cover of apersonal computer 300, which is an example of an information processingapparatus in which, the image pickup optical system of the presentinvention is built-in as an objective optical system, is opened;

FIG. 19 is a cross-sectional view of a photographic optical system 303of the personal computer 300;

FIG. 20 is a side view of the personal computer 300;

FIG. 21A, FIG. 21B, and FIG. 21C are diagrams showing a cellular phonewhich is an example of an information processing apparatus in which, theimage pickup optical system of the present invention is built-in as aphotographic optical system, where, FIG. 21A is a front view of acellular phone 400, FIG. 21B is a side view of the cellular phone 400,and FIG. 21C is a cross-sectional view of a photographic optical system405; and

FIG. 22 is a diagram explaining a sag amount.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Prior to describing embodiments, an action and an effect of an imagepickup optical system of the embodiment will be described below.

The image pickup optical system which is formed of five lenses, includesin order from an object side

a first lens having a positive refracting power,

a second lens having a negative refracting power,

a third lens having a positive refracting power,

a fourth lens having positive refracting power, and

a fifth lens having a negative refracting power,

in which the image pickup optical system has a fixed focal length, anair space is provided between the second lens and the third lens, and atleast one of surfaces of the fifth lens has an inflection point.

In the image pickup optical system of the embodiment, the aperture isdisposed nearest to the object side. Therefore, an exit pupil can bekept away from an image surface. Accordingly, at an image formingposition (an image pickup surface of an electronic image pickupelement), it is possible to make small an angle of incidence of lightrays incident on a peripheral portion. Consequently, it is possible tomake short an optical length, and to avoid degradation of a sensitivityof a peripheral portion of the image pickup element.

Moreover, since it is possible to dispose a position of principal pointsmore toward the object side of the optical system, it becomes possibleto make small the overall length sufficiently, with respect to a focallength. Accordingly, it is possible to realizing a shortening of theoverall length of the optical system.

Moreover, by making a five-lens structure by disposing the third lenshaving the positive refracting power, and letting the fourth lens to bepositive, correction of a chromatic aberration of magnification in theperipheral portion becomes advantageous, as compared to a conventionalimage pickup optical system having a four-lens structure.

Moreover, it is desirable that the image pickup optical system of theembodiment satisfies the following conditional expression.0.36<f4/f<3.88  (1)

where,

f4 denotes a focal length of the fourth lens, and

f denotes a focal length of the overall image pickup optical system.

The conditional expression (1) regulates a distribution of therefracting power of the fourth lens and the overall image pickup opticalsystem. By satisfying the conditional expression (1), the shortening ofthe overall length of the optical system and favorable aberrationcorrection are possible.

When an upper limit value in the conditional expression (1) issurpassed, the refracting power of the fourth lens becomes small. As aresult, when the shortening of the overall length of the optical systemis implemented, securing of telecentricity becomes difficult, andtherefore it is not preferable.

When a lower limit value in the conditional expression (1) is surpassed,since the refracting power of the fourth lens becomes excessivelysubstantial, a longitudinal chromatic aberration increases, andaberration correction becomes difficult.

Instead of the conditional expression (1), the following conditionalexpression (1′) may be satisfied.0.47<f4/f<2.91  (1′)

Instead of the conditional expression (1), the following conditionalexpression (1″) may be satisfied.0.55<f4/f<2.52  (1″)

Moreover, it is desirable that the image pickup optical system of theembodiment satisfies the following conditional expression.0.81<f3/f4<3.25  (2)

where,

f3 denotes a focal length of the third lens, and

f4 denotes the focal length of the fourth lens.

The conditional expression (2) regulates a distribution of therefracting power of the third lens and the fourth lens. By satisfyingthe conditional expression (2), it is possible to reduce degradation ofa decentration sensitivity caused by shortening of the overall opticalsystem, and to correct a curvature of field favorably.

When an upper limit value in the conditional expression (2) issurpassed, the refracting power of the fourth lens becomes remarkablysubstantial as compared to the refracting power of the third lens.Therefore, as the decentration sensitivity of the fourth lens becomeshigh, it is not preferable.

When a lower limit value in the conditional expression (2) is surpassed,the refracting power of the third lens becomes remarkably substantial ascompared to the refracting power of the fourth lens. Therefore, as thedecentration sensitivity of the third lens becomes high, it is notpreferable.

When it is out of a range of the conditional expression (2), as thecorrection of Petzval's sum, or in other words, the correction of thecurvature of field becomes difficult, it is not preferable.

Instead of the conditional expression (2), the following conditionalexpression (2′) may be satisfied.1.07<f3/f4<2.44  (2′)

Instead of the conditional expression (2), the following conditionalexpression (2″) may be satisfied.1.24<f3/f4<2.11  (2″)

Moreover, it is desirable that the image pickup optical system accordingto the embodiment satisfies the following conditional expression.0.28<f1/f<1.23  (3)

where,

f1 denotes a focal length of the first lens, and

f denotes a focal length of the overall image pickup optical system.

The conditional expression (3) regulates a distribution of therefracting power of the first lens and the overall image pickup opticalsystem. By satisfying the conditional expression (3), it is possible tomake short the overall length of the optical system, and to carry outfavorable aberration correction.

When a lower limit value in the conditional expression (3) is surpassed,the refracting power of the first lens becomes strong. In this case,there is an increase in various aberrations, and the aberrationcorrection becomes difficult. Moreover, as manufacturing sensitivitybecomes low, it is not preferable.

When an upper limit value in the conditional expression (3) issurpassed, the refracting power of the first lens becomes weak. In thiscase, as the shortening of the overall length of the optical systembecomes difficult, it is not preferable.

Instead of the conditional expression (3), the following conditionalexpression (3′) may be satisfied.0.51<f1/f<0.77  (3′)

Instead of the conditional expression (3), the following conditionalexpression (3″) may be satisfied.0.52<f1/f<0.64  (3″)

Moreover, in the image pickup optical system of the embodiment, it isdesirable that a surface on an image surface side of the second lens isa meniscus shaped surface which is concave toward the image side.

By letting the surface on the image surface side of the second lens tobe concave shaped toward the image surface side, and to have a negativerefracting power, shortening of the overall length of the optical systembecomes possible while making substantial an angle of emergence of lightrays and securing telecentricity.

Moreover, in the image pickup optical system of the embodiment, it isdesirable that a surface on the object side of the third lens has aconcave shape or a convex shape toward the object side. By making thesurface on the object side of the third lens concave shaped toward theobject side, it is possible to suppress an image-plane variation due toa shift in a position of the lens at the time of manufacturing, and themanufacturing sensitivity becomes low.

Moreover, by making the surface on the object side of the third lensconvex shaped toward the object side, it becomes advantageous forcorrection of the chromatic aberration of magnification.

Moreover, in the image pickup optical system of the embodiment, it isdesirable that the following conditional expression is satisfied.0.57<f3/f<6.31  (4)

where,

f3 denotes a focal length of the third lens, and

f denotes a focal length of the overall image pickup optical system.

The conditional expression (4) regulates a distribution of the thirdlens and the overall image pickup optical system. By satisfying theconditional expression (4), favorable aberration correction is possible.More elaborately, in the third lens, by suppressing appropriately aparaxial refracting power, it is possible to suppress an increase in alongitudinal chromatic aberration, and to correct the curvature of fieldfavorably.

When a lower limit value in the conditional expression (4) is surpassed,the refracting power of the third lens becomes strong. In this case, thelongitudinal chromatic aberration increases and the aberrationcorrection becomes difficult.

When an upper limit value in the conditional expression (4) issurpassed, the refracting power of the third lens becomes weak. In thiscase, the overall length of the optical system becomes long.

Instead of the conditional expression (4), the following conditionalexpression (4′) may be satisfied.1.68<f3/f<4.73  (4′)

Instead of the conditional expression (4), the following conditionalexpression (4″) may be satisfied.1.78<f3/f<4.06  (4″)

Moreover, in the image pickup optical system of the embodiment, it isdesirable that the fourth lens has a meniscus shape which is concave onthe object side and convex on the image side. By making the fourth lensmeniscus shaped which is concave on the object side and convex on theimage side, it is advantageous for correction of the coma aberrationwhile concentricity is not impaired, or in other words, whilemaintaining a state in which, a curvature center is near the aperture.

Moreover, it is desirable that the image pickup optical system of theembodiment satisfies the following conditional expression.0<|(SAG4AS−SAG4AA)/4AR|<0.147  (5)0<|(SAG4BS−SAG4BA)/4BR|<0.395  (6)

where,

SAG4AS denotes a sag amount at a position which is 60% of an effectivediameter, when a surface on the object side of the fourth lens is let tobe a spherical surface,

SAG4AA denotes a sag amount at a position which is 60% of an effectivediameter of the surface on the object side of the fourth lens,

SAG4BS denotes a sag amount at a position which is 60% of an effectivediameter when a surface on an image pickup surface side of the fourthlens is let to be a spherical surface,

SAG4BA denotes a sag amount at a position which is 60% of an effectivediameter of the surface on the image pickup surface side of the fourthlens,

4AR denotes a paraxial radius of curvature of the surface on the objectside of the fourth lens, and

4BR denotes a paraxial radius of curvature of the surface on the imagepickup surface side of the fourth lens.

Here, the sag amount will be described by referring to FIG. 22. ‘Sagamount at a position which is 60% of an effective diameter, when a lenssurface is let to be a spherical surface’ means, a distance P between areference spherical surface shown by a dotted line and a plane P passingthrough a plane apex (vertex) V, in a direction along a directionparallel to an optical axis at a position (height) which is 60% of theeffective diameter is called as SAG s.

Moreover, ‘sag amount at a position which is 60% of an effectivediameter of the lens surface’ means, a distance P between a lens surfaceshown by the dotted line and a plane P passing through the plane apex(vertex) V, in a direction along a direction parallel to the opticalaxis at a position (height) which is 60% of the effective diameter iscalled as SAG a.

The conditional expressions (5) and (6) regulate conditions preferablefor suppressing a variation in the curvature of field due to a variationin an object distance.

When an upper limit value in the conditional expressions (5) and (6) issurpassed, a substantial difference is there in longitudinal andoff-axis refracting power, and as the variation in the curvature offield due to the variation in the object distance becomes remarkable, itis not preferable.

Instead of the conditional expressions (5) and (6), the followingconditional expressions (5′) and (6′) may be satisfied.0<|(SAG4AS−SAG4AA)/4AR|<0.091  (5′)0<|(SAG4BS−SAG4BA)/4BR|<0.197  (6′)

Instead of the conditional expressions (5) and (6), the followingconditional expressions (5″) and (6″) may be satisfied.0<|(SAG4AS−SAG4AA)/4AR|<0.074  (5″)0<|(SAG4BS−SAG4BA)/4BR|<0.059  (6″)

Moreover, in the image pickup optical system of the embodiment, it isdesirable that a surface on the object side of the fifth lens is concaveshaped toward the object side.

By making the surface on the object side of the fifth lens concaveshaped, it is possible to carry out advantageously the correction of thecurvature of field and the correction of distortion, while making lightrays on an emergence side to be parallel to the optical axis.

Moreover, in the image pickup optical system of the embodiment, it isdesirable that the first lens, the second lens, the third lens, thefourth lens, and the fifth lens are formed of resin.

By using a resin as a material for the lenses, it is possible to providea low-cost image pickup optical system.

Moreover, an image pickup apparatus of the embodiment includes

the abovementioned image pickup optical system, and

an electronic image pickup element having an image pickup surface, and

satisfies the following conditional expression15°<αi<30°  (7)

where,

αi denotes an angle of incidence of principal light rays on an imagepickup surface at the maximum image height.

In a case of using a CCD (Charge Coupled Device) as the electronic imagepickup element, when off-axis light beam emerged from the optical systemmakes a large (substantial) angle with respect to an image pickupsurface, a brightness of image in a central portion and a peripheralportion of the image changes. Moreover, when an angle of incidence atthe image pickup surface is small, the problem of the change in thebrightness is solved but, the overall length of the optical systembecomes long.

When the conditional expression (7) is satisfied, it is possible tosuppress non-uniformity of the brightness of the image at the centralportion and the peripheral portion of the image, while suppressing theoverall length of the optical system from becoming long.

Moreover, in the image pickup apparatus of the embodiment, it isdesirable to have a shutter mechanism nearest to the object side of theimage pickup optical system.

By disposing the shutter nearest to the object side of the image pickupoptical system, it is possible to form the entire optical system and theshutter mechanism separately. Therefore, assembling of an image pickupmodule becomes easy, and it is advantageous for small sizing of theimage pickup module. Moreover, by disposing near the aperture stop, itis possible to reduce an effect of shutter shading.

Moreover, in the image pickup apparatus of the embodiment, it isdesirable that the image pickup optical system includes an auto-focusmechanism.

By mounting the auto-focus mechanism, it is possible to focus on anobject at any distance.

Moreover, in the image pickup apparatus of the embodiment, it isdesirable that the image pickup optical system and the electronic imagepickup element are integrated.

By integrating the electronic image pickup element, it is possible toconvert an optical image formed by the image pickup optical system intoan electric signal. Moreover, by selecting an electronic image pickupelement which is capable of reducing the change in the brightness of theimage at the central portion and the peripheral portion of the image by(due to) αi, it is possible to provide an image pickup apparatus havinga small size and an improved performance.

Moreover, in the image pickup optical system of the embodiment, it isdesirable that both surfaces of the first lens are aspheric surfaces.This is advantageous for correction of various aberrations.Particularly, this is advantageous for correction of a sphericalaberration, a coma aberration, and an astigmatism.

Furthermore, in the image pickup optical system of the embodiment, it isdesirable that both surfaces of the second lens are aspheric surfaces.This is advantageous for correction of various aberrations.Particularly, this is advantageous for correction of the sphericalaberration, the coma aberration, and the astigmatism.

Moreover, in the image pickup optical system of the embodiment, it isdesirable that both surfaces of the fourth lens are aspheric surfaces.This is advantageous for correction of various aberrations.Particularly, this is advantageous for correction of an aberration of acurvature of field, the coma aberration, and the astigmatism.

In the image pickup optical system of the present invention, it isdesirable that both surfaces of the fifth lens are aspheric surfaces.This is advantageous for correction of various aberrations.Particularly, this is advantageous for correction of the curvature offield and the astigmatism. Moreover, this is advantageous for securing aso-call telecentricity which is a state in which, light rays on anemergence side are parallel to the optical axis.

Exemplary embodiments of the image pickup optical system and theelectronic image pickup apparatus of the embodiment will be describedbelow in detail by referring to the accompanying diagrams. However, thepresent invention is not restricted to the embodiments described below.

Next, an image pickup optical system according to a first embodimentwill be described below. FIG. 1 is a cross-sectional view along anoptical axis showing an optical arrangement at a time of infinite objectpoint focusing of an image pickup optical system according to a firstembodiment.

FIG. 2 is a diagram showing a spherical aberration (SA), an astigmatism(AS), a distortion (DT), and a chromatic aberration of magnification(CC) at the time of infinite object point focusing of the image pickupoptical system according to the first embodiment. Moreover, FIY denotesan image height. Reference numerals in aberration diagrams are same inthe embodiments which will be described later.

The image pickup optical system according to the first embodiment, asshown in FIG. 1, in order from the object side, includes an aperturestop S, a first lens L1 having a positive refracting power, a secondlens L2 having a negative refracting power, a third lens L3 having apositive refracting power, a fourth lens L4 having a positive refractingpower, and a fifth lens L5 having a negative refracting power. In allthe following embodiments, in lens cross-sectional views, CG denotes acover glass, and I denotes an image pickup surface of the electronicimage pickup element.

The first lens L1 is a biconvex positive lens. The second lens L2 is abiconcave negative lens. The third lens L3 is a positive meniscus lenshaving a convex surface directed toward the object side. The fourth lensL4 is a positive meniscus lens having a convex surface directed towardthe image side. The fifth lens L5 is a biconcave negative lens.

An aspheric surface is provided to both surfaces of all the five lensesL1 to L5.

An image pickup optical system according to a second embodiment, asshown in FIG. 3, in order from the object side, includes an aperturestop S, a first lens L1 having a positive refracting power, a secondlens L2 having a negative refracting power, a third lens L3 having apositive refracting power, a fourth lens L4 having a positive refractingpower, and a fifth lens L5 having a negative refracting power.

The first lens L1 is a biconvex positive lens. The second lens L2 is anegative meniscus lens having a convex surface directed toward theobject side. The third lens L3 is a positive meniscus lens having aconvex surface directed toward the image side. The fourth lens L4 is apositive meniscus lens having a convex surface directed toward the imageside. The fifth lens L5 is a negative meniscus lens having a convexsurface directed toward the image side.

An aspheric surface is provided to both surfaces of all the five lensesL1 to L5.

An image pickup optical system according to a third embodiment, as shownin FIG. 5, in order from the object side, includes an aperture stop S, afirst lens L1 having a positive refracting power, a second lens L2having a negative refracting power, a third lens L3 having a positiverefracting power, a fourth lens L4 having a positive refracting power,and a fifth lens L5 having a negative refracting power.

The first lens L1 is a biconvex positive lens. The second lens L2 is anegative meniscus lens having a convex surface directed toward theobject side. The third lens L3 is a positive meniscus lens having aconvex surface directed toward the image side. The fourth lens L4 is apositive meniscus lens having a convex surface directed toward the imageside. The fifth lens L5 is a negative meniscus lens having a convexsurface directed toward the image side.

An aspheric surface is provided to both surfaces of all the five lensesL1 to L5.

An image pickup optical system according to a fourth embodiment, asshown in FIG. 7, in order from the object side, includes an aperturestop S, a first lens L1 having a positive refracting power, a secondlens L2 having a negative refracting power, a third lens L3 having apositive refracting power, a fourth lens L4 having a positive refractingpower, and a fifth lens L5 having a negative refracting power.

The first lens L1 is a biconvex positive lens. The second lens L2 is anegative meniscus lens having a convex surface directed toward theobject side. The third lens L3 is a biconvex positive lens. The fourthlens L4 is a positive meniscus lens having a convex surface directedtoward the image side. The fifth lens L5 is a negative meniscus lenshaving a convex surface directed toward the image side.

An aspheric surface is provided to both surfaces of all the five lensesL1 to L5.

An image pickup optical system according to a fifth embodiment, as shownin FIG. 9, in order from the object side, includes an aperture stop S, afirst lens L1 having a positive refracting power, a second lens L2having a negative refracting power, a third lens L3 having a positiverefracting power, a fourth lens L4 having a positive refracting power,and a fifth lens L5 having a negative refracting power.

The first lens L1 is a biconvex positive lens. The second lens L2 is anegative meniscus lens having a convex surface directed toward theobject side. The third lens L3 is a positive meniscus lens having aconvex surface directed toward the image side. The fourth lens L4 is apositive meniscus lens having a convex surface directed toward the imageside. The fifth lens L5 is a negative meniscus lens having a convexsurface directed toward the image side.

An aspheric surface is provided to both surfaces of all the five lensesL1 to L5.

An image pickup optical system according to a sixth embodiment, as shownin FIG. 11, in order from the object side, includes an aperture stop S,a first lens L1 having a positive refracting power, a second lens L2having a negative refracting power, a third lens L3 having a positiverefracting power, a fourth lens L4 having a positive refracting power,and a fifth lens L5 having a negative refracting power.

The first lens L1 is a biconvex positive lens. The second lens L2 is anegative meniscus lens having a convex surface directed toward theobject side. The third lens L3 is a biconvex positive lens. The fourthlens L4 is a positive meniscus lens having a convex surface directedtoward the image side. The fifth lens L5 is a biconcave negative lens.

An aspheric surface is provided to both surfaces of all the five lensesL1 to L5.

An image pickup optical system according to a seventh embodiment, asshown in FIG. 13, in order from the object side, includes an aperturestop S, a first lens L1 having a positive refracting power, a secondlens L2 having a negative refracting power, a third lens L3 having apositive refracting power, a fourth lens L4 having a positive refractingpower, and a fifth lens L5 having a negative refracting power.

The first lens L1 is a biconvex positive lens. The second lens L2 is anegative meniscus lens having a convex surface directed toward theobject side. The third lens L3 is a positive meniscus lens having aconvex surface directed toward the image side. The fourth lens L4 is apositive meniscus lens having a convex surface directed toward the imageside. The fifth lens L5 is a biconcave negative lens.

An aspheric surface is provided to both surfaces of the first lens L1,the second lens L2, the fourth lens L4, and the fifth lens L5, and asurface on the image side of the third lens L3.

Numerical data of each embodiment described above is shown below. Apartfrom symbols described above, f denotes a focal length of the overallimage pickup optical system, F_(NO) denotes an F number, ω denotes ahalf angle of field, WE denotes a wide angle end, ST denotes anintermediate state, TE denotes a telephoto end, each of r1, r2, . . .denotes radius of curvature of each lens surface, each of d1, d2, . . .denotes a distance between two lenses, each of nd1, nd2, . . . denotes arefractive index of each lens for a d-line, and each of νd1, νd2, . . .denotes an Abbe's number for each lens, Fno. denotes F number, f denotesa focal length of total optical system, * denotes an aspheric surface.

When z is let to be an optical axis with a direction of traveling oflight as a positive (direction), and y is let to be in a directionorthogonal to the optical axis, a shape of the aspheric surface isdescribed by the following expression.z=(y ² /r)/[1+{1−(K+1)(y/r)²}^(1/2) ]+A ₄ y ⁴ +A ₆ y ⁶ +A ₈ y ⁸ +A ₁₀ y¹⁰ +A ₁₂ y ¹²

where, r denotes a paraxial radius of curvature, K denotes a conicalcoefficient, A4, A6, A8, A10, and A₁₂ denote aspherical surfacecoefficients of a fourth order, a sixth order, an eight order, a tenthorder, and a twelfth order respectively. Moreover, in the asphericalsurface coefficients, ‘e−n’ (where, n is an integral number) indicates‘10^(−n)’.

“S” means that the surface is an aperture stop.

EXAMPLE 1

unit mm Surface data Surface no. r d nd νd object plane ∞ ∞  1(S) ∞−0.16  2* 1.514 0.61 1.53071 55.71  3* −8.512 0.06  4* −77.883 0.301.63260 23.28  5* 2.165 0.39  6* 2.008 0.31 1.58393 30.22  7* 2.362 0.64 8* −5.337 0.56 1.53071 55.71  9* −1.247 0.47 10* −1.175 0.55 1.5307155.71 11* 52.979 0.25 12 ∞ 0.20 1.51633 64.14 13 ∞ 0.32 Image plane ∞(Light receiving surface) Aspherical surface data 2nd surface k = 0.437A4 = −1.52719e−02, A6 = −2.10431e−02 3rd surface k = 7.266 A4 =1.32557e−01, A6 = −1.59129e−02 4th surface k = 1.079 A4 = 1.22858e−01,A6 = 4.14234e−02, A8 = −2.33656e−02 5th surface k = 3.268 A4 =−5.43689e−02, A6 = 1.07848e−01, A8 = −5.00662e−02 6th surface k =−11.164 A4 = 5.89647e−03, A6 = −4.95146e−02, A8 = 3.70178e−02, A10 =−1.95327e−02 7th surface k = 0.009 A4 = −9.63662e−02, A6 = 2.41469e−02,A8 = −1.08413e−02 8th surface k = 0.562 A4 = −8.57895e−02, A6 =3.88476e−02, A8 = −2.04390e−02 9th surface k = −1.040 A4 = −2.78432e−03,A6 = 2.26031e−02, A8 = 3.85116e−03, A10 = −2.11278e−03 10th surface k =−1.147 A4 = 7.76084e−02, A6 = −7.56962e−03, A8 = 1.86176e−04, A10 =5.78786e−07 11th surface k = −99.772 A4 = −2.96309e−02, A6 =7.64446e−04, A8 = −2.13386e−04, A10 = 3.93374e−07 Numerical data fb (inair) 0.71 Lens total length (in air) 4.59 Total system (fixed) 4.23focal length

EXAMPLE 2

unit mm Surface data Surface no. r d nd νd object plane ∞ ∞  1(S) ∞−0.15  2* 1.562 0.62 1.54454 55.93  3* −5.723 0.04  4* 5.330 0.331.63494 23.91  5* 1.462 0.29  6* −41.633 0.34 1.60352 28.21  7* −6.4590.51  8* −2.971 0.33 1.60352 28.21  9* −1.697 0.58 10* −1.453 0.811.54454 55.93 11* −7.483 0.25 12 ∞ 0.20 1.51633 64.14 13 ∞ 0.31 Imageplane ∞ (Light receiving surface) Aspherical surface data 2nd surface k= −0.251 A4 = −6.57688e−03, A6 = −1.08256e−02, A8-2.88799e−02, A10 =−5.91158e−03 3rd surface k = 5.554 A4 = 6.34805e−02, A6 = −1.12391e−01,A8 = 1.01639e−01, A10 = −5.33485e−02 4th surface k = −171.109 A4 =5.52591e−02, A6 = −5.59237e−02, A8 = 1.30568e−01, A10 = −5.13041e−02 5thsurface k = −0.238 A4 = −1.73099e−01, A6 = 2.88831e−01, A8 =−2.17465e−01, A10 = 1.23197e−01 6th surface k = 43.598 A4 =−8.87746e−02, A6 = −7.59662e−02, A8 = 2.87338e−01, A10 = −1.19189e−017th surface k = 25.501 A4 = −5.60907e−02, A6 = −6.79959e−02, A8 =1.24828e−01, A10 = 3.11344e−02 8th surface k = 0.363 A4 = −4.35137e−02,A6 = −4.64459e−02, A8 = −8.27315e−03, A10 = 1.12264e−03 9th surface k =0.173 A4 = 6.74807e−02, A6 = 1.99499e−02, A8 = −6.40927e−03, A10 =1.56685e−03 10th surface k = −1.578 A4 = 5.99798e−02, A6 = −8.31077e−03,A8 = 7.03202e−04, A10 = −5.05168e−05 11th surface k = −200.000 A4 =−2.41208e−02, A6 = −7.90557e−04, A8 = −3.92103e−04, A10 = 4.61755e−05Numerical data fb (in air) 0.69 Lens total length (in air) 4.54 Totalsystem (fixed) 4.28 focal length

EXAMPLE 3

unit mm Surface data Surface no. r d nd νd object plane ∞ ∞  1(S) ∞−0.10  2* 1.618 0.62 1.53071 55.71  3* −4.961 0.05  4* 5.710 0.331.63494 23.91  5* 1.563 0.39  6* −3.756 0.39 1.53071 55.71  7* −2.0610.42  8* −1.845 0.50 1.60352 28.21  9* −1.580 0.73 10* −1.614 0.671.53071 55.71 11* −7.980 0.25 12  ∞ 0.20 1.51633 64.14 13  ∞ 0.31 Imageplane ∞ (Light receiving surface) Aspherical surface data 2nd surface k= −0.170 A4 = −1.00356e−02, A6 = −3.81996e−03, A8 = 5.51225e−03, A10 =−2.99796e−03 3rd surface k = 7.114 A4 = 7.85575e−02, A6 = 1.21370e−02,A8 = 5.33615e−03, A10 = 1.31206e−02 4th surface k = −113.321 A4 =6.01996e−02, A6 = 4.26326e−03, A8 = 1.30646e−01, A10 = −9.05304e−02 5thsurface k = 0.790 A4 = −1.32069e−01, A6 = 1.44559e−01, A8 =−6.94869e−02, A10 = 2.98790e−02 6th surface k = −22.022 A4 =−1.85512e−02, A6 = 6.79936e−02, A8 = 8.52940e−04, A10 = 4.87794e−04 7thsurface k = −5.915 A4 = 1.50114e−02, A6 = 6.95824e−02, A8 =−5.46294e−04, A10 = −2.72286e−03 8th surface k = −2.318 A4 =1.39851e−02, A6 = 9.33341e−02, A8 = −1.01201e−01, A10 = 3.11984e−02, A12= −2.96310e−03 9th surface k = −0.109 A4 = 4.90824e−02, A6 =8.55630e−02, A8 = −4.72267e−02, A10 = 8.61669e−03, A12 = 1.97114e−0410th surface k = −1.005 A4 = 5.28628e−02, A6 = −5.86815e−03, A8 =8.46175e−04, A10 = −8.07449e−05, A12 = 3.71532e−07 11th surface k =−445.082 A4 = −2.58354e−02, A6 = 1.51787e−03, A8 = −3.84860e−04, A10 =2.54376e−05, A12 = 9.34150e−08 Numerical data fb (in air) 0.71 Lenstotal length (in air) 4.82 Total system (fixed) focal length 4.47

EXAMPLE 4

unit mm Surface data Surface no. r d nd νd object plane ∞ ∞  1(S) ∞−0.18  2* 1.449 0.55 1.53071 55.71  3* −6.171 0.06  4* 5.948 0.331.63494 23.91  5* 1.443 0.28  6* 19.919 0.34 1.60352 28.21  7* −19.9910.43  8* −2.719 0.34 1.60352 28.21  9* −1.699 0.70 10* −1.722 0.811.53071 55.71 11* −11.154 0.25 12  ∞ 0.20 1.51633 64.14 13  ∞ 0.33 Imageplane ∞ (Light receiving surface) Aspherical surface data 2nd surface k= −0.117 A4 = −1.18556e−03, A6 = −6.58231e−03, A8 = −2.32639e−02, A10 =3.01692e−02 3rd surface k = −11.751 A4 = 7.53795e−02, A6 = −9.31862e−02,A8 = 1.10250e−01, A10 = 4.78478e−03 4th surface k = −174.630 A4 =4.88256e−02, A6 = −5.68098e−02, A8 = 1.46920e−01, A10 = −3.82802e−02 5thsurface k = −0.092 A4 = −1.63449e−01, A6 = 2.78687e−01, A8 =−2.54070e−01, A10 = 1.68844e−01 6th surface k = 41.914 A4 =−7.82489e−02, A6 = −5.97126e−02, A8 = 2.95170e−01, A10 = −1.61574e−017th surface k = 101.771 A4 = −6.86789e−02, A6 = −8.41227e−02, A8 =1.10130e−01, A10 = 3.83175e−02 8th surface k = 0.915 A4 = −4.70200e−02,A6 = −6.88395e−02, A8 = −2.66452e−03, A10 = −2.39501e−02 9th surface k =0.332 A4 = 6.15674e−02, A6 = 2.48501e−02, A8 = −4.90039e−03, A10 =2.29803e−03 10th surface k = −1.112 A4 = 5.82775e−02, A6 = −7.14819e−03,A8 = 6.34866e−04, A10 = −4.04834e−05 11th surface k = −636.320 A4 =−2.12631e−02, A6 = −1.50144e−03, A8 = −4.38711e−04, A10 = 6.36103e−05Numerical data fb (in air) 0.71 Lens total length (in air) 4.55 Totalsystem (fixed) focal length 4.37

EXAMPLE 5

unit mm Surface data Surface no. r d nd νd object plane ∞ ∞ 1(S) ∞ −0.102* 1.566 0.55 1.54454 55.93 3* −13.551 0.06 4* 6.440 0.33 1.63494 23.915* 1.754 0.33 6  −10.574 0.47 1.53071 55.71 7* −3.536 0.43 8* −2.4420.57 1.54454 55.93 9* −1.247 0.70 10*  −1.071 0.41 1.54454 55.93 11* −4.779 0.30 12  ∞ 0.20 1.51633 64.14 13  ∞ 0.30 Image plane ∞ (Lightreceiving surface) Aspherical surface data 2nd surface k = 0.118 A4 =3.51981e−03, A6 = 3.15415e−04, A8 = 2.85742e−02 3rd surface k = −49.163A4 = 9.91226e−02, A6 = −1.01062e−01, A8 = 1.87672e−01 4th surface k =6.287 A4 = 4.22317e−02, A6 = −1.42760e−01, A8 = 2.38264e−01, A10 =−3.19567e−02 5th surface k = 1.391 A4 = −6.20887e−02, A6 = 2.25292e−02,A8 = −9.94067e−02, A10 = 1.30287e−01 7th surface k = −3.816 A4 =1.98999e−02, A6 = −5.49857e−02, A8 = 2.73220e−02, A10 = 1.14483e−02 8thsurface k = 1.870 A4 = −5.96485e−02, A6 = 1.39147e−01, A8 =−1.30303e−01, A10 = 4.49195e−02 9th surface k = −0.461 A4 =−2.79628e−03, A6 = 1.03908e−01, A8 = −3.66048e−02, A10 = 6.17661e−0310th surface k = −1.885 A4 = 5.81773e−02, A6 = −6.68551e−03, A8 =1.30080e−04, A10 = 8.02451e−06, A12 = 8.92094e−07 11th surface k =−150.548 A4 = −1.68889e−02, A6 = 5.44836e−04, A8 = −5.25831e−04, A10 =1.26296e−04, A12 = −1.02406e−05 Numerical data fb (in air) 0.76 Lenstotal length (in air) 4.61 Total system (fixed) 4.09 focal length

EXAMPLE 6

unit mm Surface data Surface no. r d nd νd object plane ∞ ∞  1(S) ∞−0.10  2* 1.895 0.70 1.54454 55.93  3* −35.770 0.05  4* 4.541 0.341.63494 23.91  5* 1.763 0.36  6* 554.313 0.49 1.53071 55.71  7* −4.9230.49  8* −2.316 0.77 1.54454 55.93  9* −1.132 0.57 10* −3.874 0.441.54454 55.93 11* 2.329 0.46 12  ∞ 0.30 1.51633 64.14 13  ∞ 0.40 Imageplane ∞ (Light receiving surface) Aspherical surface data 2nd surface k= −0.417 A4 = 2.30722e−02, A6 = −1.57621e−02, A8 = 2.42845e−02 3rdsurface k = 0.027 A4 = 8.14577e−04, A6 = 3.23114e−02, A8 = 1.84596e−024th surface k = −41.241 A4 = −5.43173e−02, A6 = 6.47387e−02, A8 =−9.99442e−03, A10 = −6.30963e−03 5th surface k = 0.803 A4 =−1.26827e−01, A6 = 8.91246e−02, A8 = −5.28834e−02, A10 = 6.13521e−03 6thsurface k = −1.264 A4 = −3.67651e−02, A6 = 4.83340e−04, A8 =2.45824e−02, A10 = −7.23457e−03 7th surface k = −3.287 A4 =−5.22028e−02, A6 = 3.97193e−02, A8 = −3.88474e−02, A10 = 1.79400e−02 8thsurface k = 1.102 A4 = −9.69947e−02, A6 = 1.27478e−01, A8 =−5.71162e−02, A10 = 1.24910e−02 9th surface k = −0.868 A4 = 3.03167e−02,A6 = 5.02812e−03, A8 = 9.35928e−03, A10 = −2.37338e−03 10th surface k =−0.243 A4 = 6.13107e−03, A6 = 2.18227e−04, A8 = 2.20085e−04, A10 =−2.21650e−05 11th surface k = −9.257 A4 = −3.71806e−02, A6 =6.26959e−03, A8 = −8.14906e−04, A10 = 4.31811e−05 Numerical data fb (inair) 1.06 Lens total length (in air) 5.28 Total system (fixed) focallength 4.32

EXAMPLE 7

unit mm Surface data Surface no. r d nd νd object plane ∞ ∞ 1(S) ∞ −0.102* 2.100 0.85 1.53071 55.71 3* −10.000 0.05 4* 9.391 0.40 1.63494 23.915* 2.428 0.76 6* −3.409 0.66 1.53071 55.71 7* −1.539 0.38 8* −1.402 0.831.53071 55.71 9* −1.300 0.66 10*  −1.908 0.50 1.53071 55.71 11*  47.4770.60 12  ∞ 0.30 1.51633 64.14 13  ∞ 0.45 Image plane ∞ (Light receivingsurface) Aspherical surface data 2nd surface k = −1.154 A4 =1.46019e−02, A6 = 8.67027e−04, A8 = −1.00000e−03 3rd surface k = −5.000A4 = 7.83820e−03, A6 = 2.24308e−04, A8 = −1.09538e−04 4th surface k =3.593 A4 = −1.93960e−02, A6 = 1.25120e−02, A8 = 5.66178e−04 5th surfacek = 1.505 A4 = −3.04522e−02, A6 = 1.15182e−02, A8 = 1.85302e−04 6thsurface k = 1.351 A4 = −1.00000e−02, A6 = 1.30000e−03 7th surface k =−1.575 A4 = 2.33107e−02, A6 = −5.69157e−03 8th surface k = −0.869 A4 =5.99547e−02, A6 = −6.95207e−03, A8 = −4.49331e−04 9th surface k = −1.259A4 = 1.00000e−02, A6 = 1.00000e−03 10th surface k = −0.818 A4 =4.38227e−02, A6 = −4.00871e−03, A8 = −2.87456e−05, A10 = 1.78791e−0511th surface k = 15.000 A4 = −8.66144e−03, A6 = 1.01133e−03, A8 =−1.84966e−04, A10 = 5.56796e−06 Numerical data fb (in air) 1.25 Lenstotal length) (in air) 6.35 Total system (fixed) focal length 5.43

Values of conditional expressions in each of embodiments are shownbelow:

Expression (1) f4/f Expression (2) f3/f4 Expression (3) f1/f Expression(4) f3/f Expression (5) |(SAG4AS − SAG4AA)/4AR| Expression (6) |(SAG4BS− SAG4BA)/4BR| Expression (7) αi

Example 1 Example 2 Example 3 Example 4 f 4.23 4.28 4.47 4.37 f1 2.462.31 2.37 2.26 f2 −3.28 −3.25 −3.47 −3.06 f3 17.13 12.52 7.94 16.45 f42.91 5.93 10.54 6.61 f5 −2.15 −3.46 −3.94 −3.94 F NO 2.80 2.80 2.94 2.94Expression (1) 0.69 1.38 2.36 1.51 Expression (2) 5.89 2.11 0.75 2.49Expression (3) 0.58 0.54 0.53 0.52 Expression (4) 4.06 2.92 1.78 3.76Expression (5) 0.005 0.004 0.013 0.004 Expression (6) 0.062 0.021 0.0400.014 Expression (7) 26 26 24 25 Example 5 Example 6 Example 7 f 4.094.32 5.43 f1 2.60 3.31 3.34 f2 −3.86 −4.72 −5.23 f3 9.74 9.16 4.68 f43.99 3.29 8.77 f5 −2.63 −2.59 −3.43 F NO 2.94 2.80 2.89 Expression (1)0.98 0.76 1.62 Expression (2) 2.44 2.78 0.53 Expression (3) 0.64 0.770.61 Expression (4) 2.38 2.12 0.86 Expression (5) 0.004 0.010 0.074Expression (6) 0.059 0.182 0.197 Expression (7) 25 24 24

Thus, it is possible to use such image pickup optical system of thepresent invention in a photographic apparatus in which an image of anobject is photographed by an electronic image pickup element such as aCCD and a CMOS, particularly a digital camera and a video camera, apersonal computer, a telephone, and a portable terminal which areexamples of an information processing unit, particularly a portabletelephone which is easy to carry. Embodiments thereof will beexemplified below.

In FIG. 15 to FIG. 17 show conceptual diagrams of structures in whichthe image pickup optical system according to the present invention isincorporated in a photographic optical system 41 of a digital camera.FIG. 15 is a frontward perspective view showing an appearance of adigital camera 40, FIG. 16 is a rearward perspective view of the same,and FIG. 17 is a cross-sectional view showing an optical arrangement ofthe digital camera 40.

The digital camera 40, in a case of this example, includes thephotographic optical system 41 (an objective optical system forphotography 48) having an optical path for photography 42, a finderoptical system 43 having an optical path for finder 44, a shutter 45, aflash 46, and a liquid-crystal display monitor 47. Moreover, when theshutter 45 disposed at an upper portion of the camera 40 is pressed, inconjugation with this, a photograph is taken through the photographicoptical system 41 (objective optical system for photography 48) such asthe image pickup optical system in the first embodiment.

An object image formed by the photographic optical system 41(photographic objective optical system 48) is formed on an image pickupsurface 50 of a CCD 49. The object image photoreceived at the CCD 49 isdisplayed on the liquid-crystal display monitor 47 which is provided ona camera rear surface as an electronic image, via an image processingmeans 51. Moreover, a memory etc. is disposed in the image processingmeans 51, and it is possible to record the electronic imagephotographed. This memory may be provided separately from the imageprocessing means 51, or may be formed by carrying out by writing byrecording (recorded writing) electronically by a floppy (registeredtrademark) disc, memory card, or an MO etc.

Furthermore, an objective optical system for finder 53 is disposed inthe optical path for finder 44. This objective optical system for finder53 includes a cover lens 54, a first prism 10, an aperture stop 2, asecond prism 20, and a lens for focusing 66. An object image is formedon an image forming surface 67 by this objective optical system forfinder 53. This object image is formed in a field frame of a Porro prismwhich is an image erecting member equipped with a first reflectingsurface 56 and a second reflecting surface 58. On a rear side of thisPorro prism, an eyepiece optical system. 59 which guides an image formedas an erected normal image is disposed.

By the digital camera 40 structured in such manner, it is possible torealize an optical image pickup apparatus having an image pickup opticalsystem with a reduced size and thickness, in which the number ofstructural components is reduced.

Next, a personal computer which is an example of an informationprocessing apparatus with a built-in image forming system as anobjective optical system is shown in FIG. 18 to FIG. 20. FIG. 18 is afrontward perspective view of a personal computer 300 with its coveropened, FIG. 19 is a cross-sectional view of a photographic opticalsystem 303 of the personal computer 300, and FIG. 20 is a side view ofFIG. 18. As it is shown in FIG. 80 to FIG. 82, the personal computer 300has a keyboard 301, an information processing means and a recordingmeans, a monitor 302, and a photographic optical system 303.

Here, the keyboard 301 is for an operator to input information from anoutside. The information processing means and the recording means areomitted in the diagram. The monitor 302 is for displaying theinformation to the operator. The photographic optical system 303 is forphotographing an image of the operator or a surrounding. The monitor 302may be a display such as a liquid-crystal display or a CRT display. Asthe liquid-crystal display, a transmission liquid-crystal display devicewhich illuminates from a rear surface by a backlight not shown in thediagram, and a reflection liquid-crystal display device which displaysby reflecting light from a front surface are available. Moreover, in thediagram, the photographic optical system 303 is built-in at a right sideof the monitor 302, but without restricting to this location, thephotographic optical system 303 may be anywhere around the monitor 302and the keyboard 301.

This photographic optical system 303 has an objective optical system 100which includes the image pickup optical system in the first embodimentfor example, and an electronic image pickup element chip 162 whichreceives an image. These are built into the personal computer 300.

At a front end of a mirror frame, a cover glass 102 for protecting theobjective optical system 100 is disposed.

An object image received at the electronic image pickup element chip 162is input to a processing means of the personal computer 300 via aterminal 166. Further, the object image is displayed as an electronicimage on the monitor 302. In FIG. 18, an image 305 photographed by theuser is displayed as an example of the electronic image. Moreover, it isalso possible to display the image 305 on a personal computer of acommunication counterpart from a remote location via a processing means.For transmitting the image to the remote location, the Internet andtelephone are used.

Next, a telephone which is an example of an information processingapparatus in which the image pickup optical system of the presentinvention is built-in as a photographic optical system, particularly aportable telephone which is easy to carry is shown in FIG. 21A, FIG.21B, and FIG. 21C. FIG. 21A is a front view of a portable telephone 400,FIG. 21B is a side view of the portable telephone 400, and FIG. 21C is across-sectional view of a photographic optical system 405. As shown inFIG. 83A to FIG. 83C, the portable telephone 400 includes a microphonesection 401, a speaker section 402, an input dial 403, a monitor 404,the photographic optical system 405, an antenna 406, and a processingmeans.

Here, the microphone section 401 is for inputting a voice of theoperator as information. The speaker section 402 is for outputting avoice of the communication counterpart. The input dial 403 is for theoperator to input information. The monitor 404 is for displaying aphotographic image of the operator himself and the communicationcounterpart, and information such as a telephone number. The antenna 406is for carrying out a transmission and a reception of communicationelectric waves. The processing means (not shown in the diagram) is forcarrying out processing of image information, communication information,and input signal etc.

Here, the monitor 404 is a liquid-crystal display device. Moreover, inthe diagram, a position of disposing each structural element is notrestricted in particular to a position in the diagram. This photographicoptical system 405 has an objective optical system 100 which is disposedin a photographic optical path 407 and an image pickup element chip 162which receives an object image. As the objective optical system 100, theimage pickup optical system in the first embodiment for example, isused. These are built into the portable telephone 400.

At a front end of a mirror frame, a cover glass 102 for protecting theobjective optical system 100 is disposed.

An object image received at the electronic image pickup element chip 162is input to an image processing means which is not shown in the diagram,via a terminal 166. Further, the object image finally displayed as anelectronic image on the monitor 404 or a monitor of the communicationcounterpart, or both. Moreover, a signal processing function is includedin the processing means. In a case of transmitting an image to thecommunication counterpart, according to this function, information ofthe object image received at the electronic image pickup element chip162 is converted to a signal which can be transmitted.

An image pickup optical system of this information processing unit,though differs from a lens cross-sectional arrangement in each of thenumerical embodiments, the image pickup optical system of each of theembodiments is mounted as described above.

The present invention may have various modified embodiments which fairlyfall within the basic teachings herein set forth.

As it has been described above, the present invention is useful for animage pickup optical system having a small size and an improvedperformance.

According to the present invention, an effect is shown that it ispossible to provide an image pickup optical system having a small sizeand an improved performance, and an image pickup apparatus whichincludes the image pickup optical system.

What is claimed is:
 1. An image pickup optical system comprising inorder from an object side: an aperture stop; a first lens having apositive refracting power; a second lens having a negative refractingpower; a third lens; a fourth lens having a positive refracting power,wherein a surface on an object side is concave shaped; and a fifth lenshaving a negative refracting power, wherein the image pickup opticalsystem has a fixed focal length, an air space is provided between thesecond lens and the third lens, and at least one of surfaces of thefifth lens has an inflection point.
 2. The image pickup optical systemaccording to claim 1, wherein the air distance is provided between eachof the lenses.
 3. The image pickup optical system according to claim 1,wherein the image pickup optical system satisfies the followingconditional expression0.28<f1/f<1.23  (1) where, f1 denotes a focal length of the first lens,and f denotes a focal length of the overall image pickup optical system.4. The image pickup optical system according to claim 1, wherein asurface on an image surface side of the second lens is concave shapedtoward the image surface side.
 5. The image pickup optical systemaccording to claim 1, wherein the image pickup optical system satisfiesthe following conditional expression0.36<f4/f<3.88  (2) where, f4 denotes a focal length of the fourth lens,and f denotes a focal length of the overall image pickup optical system.6. The image pickup optical system according to claim 1, wherein theimage pickup optical system satisfies the following conditionalexpression1.3<L5maxt/d10<2.35  (3) where, L5maxt denotes a maximum thickness alonga parallel to an optical axis within effective aperture of the fifthlens, and d10 denotes thickness along the optical axis of the fifthlens.
 7. The image pickup optical system according to claim 1, whereinat paraxial area of surface on the image side of the fifth lens is aconcave shaped lens.
 8. The image pickup optical system according toclaim 1, wherein the image pickup optical system satisfies the followingconditional expression0.15<BF/TTL<0.25  (5) where, BF denotes a distance on the optical axisbetween image side surface and image pickup surface of the fifth lens,TTL denotes a total length of the image pickup optical system.
 9. Theimage pickup optical system according to claim 1, wherein the imagepickup optical system satisfies the following conditional expression0.15<BF/TTL<0.22  (4) where, BF denotes a distance on the optical axisbetween image side surface and image pickup surface of the fifth lens,TTL denotes a total length of the image pickup optical system.
 10. Theimage pickup optical system according to claim 1, wherein the firstlens, the second lens, the third lens, the fourth lens, and the fifthlens are formed of a resin.
 11. The image pickup optical systemaccording to claim 1, wherein the image pickup apparatus satisfies thefollowing conditional expression15°<αi<45°  (7) where, αi denotes an angle of incidence of principallight rays on an image pickup surface at the maximum image height. 12.The image pickup optical system according to claim 1, wherein anelectronic image pickup element having an image pickup surface, whereinthe image pickup apparatus satisfies the following conditionalexpression15°<αi<30°  (6) where, αi denotes an angle of incidence of principallight rays on an image pickup surface at the maximum image height. 13.An image pickup apparatus comprising: an image pickup optical system; anelectronic image pickup element having an image pickup surface toreceive an image from the image pickup optical system, wherein the imagepickup optical system comprising in order from an object side: anaperture stop; a first lens having a positive refracting power; a secondlens having a negative refracting power; a third lens; a fourth lenshaving a positive refracting power, wherein a surface on an object sideis concave shaped; and a fifth lens having a negative refracting power,wherein the image pickup optical system has a fixed focal length, an airspace is provided between the second lens and the third lens, and atleast one of surfaces of the fifth lens has an inflection point.
 14. Theimage pickup apparatus according to claim 13, further comprising: ashutter mechanism which is nearest to the object side of the imagepickup optical system.
 15. The image pickup apparatus according to claim13, wherein the image pickup optical system includes an auto-focusmechanism.
 16. The image pickup apparatus according to claim 13, whereinthe air distance is provided between the each lens in the image pickupoptical system.
 17. The image pickup apparatus according to claim 13,wherein the image pickup optical system satisfies the followingconditional expression0.28<f1/f<1.23  (1) where, f1 denotes a focal length of the first lens,and f denotes a focal length of the overall image pickup optical system.18. The image pickup apparatus according to claim 13, wherein a surfaceon an image surface side of the second lens is concave shaped toward theimage surface side in the image pickup optical system.
 19. The imagepickup apparatus according to claim 13, wherein the image pickup opticalsystem satisfies the following conditional expression0.36<f4/f<3.88  (2) where, f4 denotes a focal length of the fourth lens,and f denotes a focal length of the overall image pickup optical system.20. The image pickup apparatus according to claim 13, wherein the imagepickup optical system satisfies the following conditional expression1.3<L5maxt/d10<2.35  (3) where, L5maxt denotes a maximum thickness alonga parallel to an optical axis within effective aperture of the fifthlens, and d10 denotes thickness of the optical axis of the fifth lens.21. The image pickup apparatus according to claim 13, wherein a surfaceon the object side at a paraxial area of the fifth lens is a concaveshaped lens.
 22. The image pickup apparatus according to claim 13,wherein the image pickup optical system satisfies the followingconditional expression0.15<BF/TTL<0.25  (5) where, BF denotes a distance on the optical axisbetween image side surface and image pickup surface of the fifth lens,TTL denotes a total length of the image pickup optical system.
 23. Theimage pickup apparatus according to claim 13, wherein the image pickupoptical system satisfies the following conditional expression0.15<BF/TTL<0.22  (4) where, BF denotes a distance on the optical axisbetween image side surface and image pickup surface of the fifth lens,TTL denotes a total length of the image pickup optical system.
 24. Theimage pickup apparatus according to claim 13, wherein the first lens,the second lens, the third lens, the fourth lens, and the fifth lens areformed of a resin.
 25. The image pickup apparatus according to claim 13,wherein the image pickup optical system satisfies the followingconditional expression15°<αi<45°  (7) where, αi denotes an angle of incidence of principallight rays on an image pickup surface at the maximum image height. 26.The image pickup optical system according to claim 13, wherein anelectronic image pickup element having an image pickup surface, whereinthe image pickup apparatus satisfies the following conditionalexpression15°<αi<30°  (6) where, αi denotes an angle of incidence of principallight rays on an image pickup surface at the maximum image height. 27.An information apparatus comprising: an input section which operates theinformation apparatus; a processing section which processes informationat least from the input section; an image pickup apparatus which obtainimage information based on information from the processing section; animage processing section which processes image information obtained bythe image pickup section; and a display section which displays theprocessed image, wherein the image pickup apparatus has an image pickupoptical system, and an electronic image pickup element having an imagepickup surface to receive the image from the image pickup opticalsystem, further, an image pickup optical system comprising in order froman object side: an aperture stop; a first lens having a positiverefracting power; a second lens having a negative refracting power; athird lens; a fourth lens having a positive refracting power, wherein asurface on an object side is concave shaped; and a fifth lens having anegative refracting power, wherein the image pickup optical system has afixed focal length, an air space is provided between the second lens andthe third lens, and at least one of surfaces of the fifth lens has aninflection point.
 28. The information apparatus according to claim 27,further comprising a communication section which able to communicate theimage information obtained by the image pickup unit.
 29. The informationapparatus according to claim 27, further comprising a sound obtainsection which able to communicate the image information obtained by theimage pickup unit.
 30. An information apparatus according to claim 27,wherein the information apparatus is a portable electronic device. 31.An information apparatus according to claim 27, wherein air distance isprovided between the each lens in the image pickup optical system. 32.The information apparatus according to claim 27, wherein the imagepickup optical system satisfies the following conditional expression0.28<f1/f<1.23  (1) where, f1 denotes a focal length of the first lens,and f denotes a focal length of the overall image pickup optical system.33. The information apparatus according to claim 27, wherein a surfaceon an image side surface of the second lens is concave shaped toward theimage surface side in the image pickup optical system.
 34. Theinformation apparatus according to claim 27, wherein the image pickupoptical system satisfies the following conditional expression0.36<f4/f<3.88  (2) f4 denotes a focal length of the fourth lens, and fdenotes a focal length of the overall image pickup optical system. 35.The information apparatus according to claim 27, wherein the imagepickup optical system according to claim 1, wherein the image pickupoptical system satisfies the following conditional expression1.3<L5maxt/d10<2.35  (3) where, L5maxt denotes a maximum thickness alonga parallel to an optical axis within effective aperture of the fifthlens, and d10 denotes thickness of the optical axis of the fifth lens.36. The information apparatus according to claim 27, wherein a surfaceon the object side at a paraxial area of the fifth lens is a concaveshaped lens.
 37. The information apparatus according to claim 27,wherein the image pickup optical system satisfies the followingconditional expression0.15<BF/TTL<0.25  (5) where, BF denotes a distance on the optical axisbetween image side surface and image pickup surface of the fifth lens,TTL denotes a total length of the image pickup optical system.
 38. Theinformation apparatus according to claim 27, wherein the image pickupoptical system satisfies the following conditional expression0.15<BF/TTL<0.25  (5) where, BF denotes a distance on the optical axisbetween image side surface and image pickup surface of the fifth lens,TTL denotes a total length of the image pickup optical system.
 39. Theinformation apparatus according to claim 27, wherein the image pickupoptical system satisfies the following conditional expression0.15<BF/TTL<0.25  (5) where, BF denotes a distance on the optical axisbetween image side surface and image pickup surface of the fifth lens,TTL denotes a total length of the image pickup optical system.
 40. Theinformation apparatus according to claim 27, wherein the first lens, thesecond lens, the third lens, the fourth lens, and the fifth lens areformed of a resin.
 41. The information apparatus according to claim 27,wherein the image pickup optical system satisfies the followingconditional expression15°<αi<45°  (7) where, αi denotes an angle of incidence of principallight rays on an image pickup surface at the maximum image height. 42.The information apparatus according to claim 27, wherein the imagepickup optical system satisfies the following conditional expression15°<αi<30°  (6) where, αi denotes an angle of incidence of principallight rays on an image pickup surface at the maximum image height.